Oil burner safety control system



April 15, 1952 P. SCHELL 2,592,827

OIL BURNER SAFETY CONTROL SYSTEM Filed Feb. 28. 1948 INVEN TOR. Pa, :(2 56%622.

Patented Apr. 15, 1952 OIL BURNER SAFETY CONTROL SYSTEM Paul Schell, Elkhart, Ind., assignor to Penn Controls, Inc., a corporation of Indiana Application February 28, 1948, Serial No. 12,030

4 Claims. (Cl. 158-28) This invention relates to an oil burner control of simple and inexpensive construction having a number of advantageous features with respect to the automatic operation of an oil burner.

One object is to provide in connection with a burner control circuit which gives low voltage protection by reason of a single relay capable of cutting in at low line voltage and out at only a slightly lower point, whereas in the usual systems in which relays are used for burner control circuits a relay that is properly designed to give sufficient motion for operation of the contacts cut out at a much lower line voltage. This is particularly important because at about 60 percent of the full line voltage the burner functions improperly, its efficiency is low, the air velocity and the oil pressure being decreased and the opening of the solenoid or pressure regulating valve (which usually controls the oil supply) is restricted. Also low voltage in the ignition transformer causes entire loss of spark or at least irregular spark. This results in the burner popping and sometimes in an explosion. The problem is particularly present in small localities where current consumption varies greatly and in most all localities when sleet gets on the transmission wires and causes a temporary drop in voltage sometimes lasting for several hours. It is therefore obvious that cut-out of the relay at a point only slightly less than its pull-in voltage is desirable.

Another object of my invention is to provide a relay which can be cut in at one voltage and thereafter maintained in the cut-in position by areduced voltage so that it is then easier to drop out upon subsequentvoltage drop and a dropping out of the relay will occur before an excessive drop in line voltage.

Still another object is to provide a control system wherein a combustion switch controls the operation of a safety switch and also a holding circuit that reduces current flow through the relay, thereby permitting the relay to drop out after only a slight drop in line voltage as distinguished from those types of relays which are energized to cut in and then maintained at that energization value, thereby requiring a greater line voltage drop before they cut out to protect the burner against faulty operation due to line voltage drop.

A further object is to provide a combustion switch which operates a holding switch and a switch for a safety switch heater in such manner that a slight rise in combustion temperature closes the holding switch and a greater rise in temperature opens the circuit of the safety switch heater so that upon flame failure the burner will shut down for a short period of time due to re-opening of the holding switch but will soon start up again due to reclosing of the safety switch heater contacts of the combustion switch which re-establish the relay circuit thus recycling the bumer if conditions are such that it can be started again. v

Still a further object is to provide means to lock the burner out of operation if-it does not re-cycle, which means consists of operation of a safety switch that requires manual re-setting before the burner can be put back into operation.

An additional object is to provide a combustion switch having two sets of contacts, one of which is always operated ahead of the other upon either temperature rise or temperature drop in the stack so that the control circuit is conditioned for re-cycling if possible due to operation of the first switch to be operated, whereas the second switch to be operated closes a circuit that operates a safety switch after a pre-determined period of time providing that combustion is not reestablished in the meantime to reverse the'operation of the combustion switch and open the operating circuit for the safety switch and re-establish the normal running circuit.

Another additional object is to provide a combustion switch operable to open an ignition circuit for the burner in the event that intermittent ignition as distinguished from continuous ignition is desired or necessary in the oil burner installation.

With these and other objects in view, my invention consists in the construction, arrangement and combination of the various parts of my oil burner control whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims and illustrated in the accompanying drawing, wherein:

Figure 1 is an electro-diagrammatic view of an oil burner control system embodying my present invention, and

Figure 2 is a sectional view on the line 2-2 of Figure 1 showing an operating connection between a temperature responsive element and a switch operating element used in my system for response to the temperature of combustion.

In the accompanying drawing I have used the reference character M to indicate a motor or the like of an oil burner, the burner being indicated generally at B. Ignition mechanism is provided .for the burner and is indicated diagrammatically at Ign. A transformer T is provided having a primary coil in and a secondary coil l2, the coil I2 having an intermediate tap [4.

A room thermostat RT is provided in the secondary circuit which circuit also includes a relay coil RC, a safety switch heater SSH and safety switch heater control contacts SC of a combustion switch indicated generally at CS. The control circuit further includes a holding switch HS which is also part of the combustion switch CS.

A normally closed safety switch SS is provided which dominates the main circuit from the current supply wires. The safety switch is adapted to be opened by energization of a safety switch heater SSH for a predetermined length of time by reason of the heater warping a bimetal element l6 upwardly to release a latch [3 which is then swung clockwise by means of a spring 29 to open the safety switch SS through a mechanical connection 22 such as alink or thrust element.

The relay R includes an armature represented at 24 which is connected with a motor switch MS adapted to control the circuit of the motor M and also the closing of the circuit for the ignition mechanism Ign. For opening the circuit of the ignition mechanism independent of the motor switch MS, I provide an ignition switch IS which is part of the combustion switch CS.

The combustion switch includes a bimetal helix 26 or other thermal element responsive to combustion temperature as for instance in the stack between the furnace and the chimney. One end of the thermal element is anchored stationary at, 28 and the other end is secured at 30 to an actuating shaft 32. This shaft is journaled in the stationary element 28 and rotates. a collar 34 which is frictionally engaged with a switch arm 36. This frictional engagement, may be in the form of a washer 38 engaged against. a second switch arm 31' which in turn is engaged against the arm 36, and a spring 40. is interposed between the washer 38 and a second washer ll retained on the shaft 32 by a key.39.

This type of connection known as a slip clutch makes the switch arms38 and 3'! responsive to change in. temperature as distinguished from being directly responsive in proportion to temperature. Accordingly the switch arms are rotated in one direction upon commencement of temperature rise to operate the switches, HS, SC and ISin one direction and after they are operated a continued rise in temperature causes the disc 34 to slip in relation to the switch arms so that upon a reversal in temperature aifecting thethermal element 2%; the switches will be operated in the opposite direction and slipping will thereafter occur.

Practical operation When the parts are in the position of Figure l the burner has just been shut OE and. is idle, the switch arms 36 and 31 having rotated counterclockwise so that the switch IS has re-clo'sed, the switch HS has re-opened and the switch SC has. re-closed. Upon further temperature drop, an actuating finger 42 at the lower end of thearm is stopped by the switch blade of the contacts SC and an opposing actuating finger M will be engaging the switch blade of the holding switch HS without however further changing the circuit through either switch.

When the room thermostat RT calls for heat a control circuit is. established from the lower end of the secondary coil I2 through SC, SSH,

RC and RT to the upper end of the coil l2, the current thus being supplied by the entire secondary. Assuming the secondary voltage to be 25 then there are 25 volts available for energizing the relay coil RC to cause cut-in of the relay. The parts can be so designed that the relay can cut in at 80 percent of this value so that the relay is thus operable at any voltage above 80 percent of the full line voltage supplied to the primary coil l9.

Energization of the relay coil RC closes the motor switch MS so that the motor M and the ignition mechanism Ign are energized thus effecting normal operation of the burner. If combustion occurs as it should, the switch operating arms 35 and 37 will rotate clockwise, the finger 45 of the arm 3'! first closing the holding switch HS so that the upper half of the secondary coil [2 is then energizing the relay coil and the lower half of the coil 12 is energizing the safety switch heater. Soon thereafter the switch finger 43 of the arm 35 will open the contacts'SC so that the safety switch heater is deenergized to prevent it from causing a safety shut-down of the system and a projection 42a of the arm 36 will open the ignition switch IS so that the ignition is cut off. The control is thus of the intermittent, ignition type whereas the switch IS can be omitted if it is to be of the continuous ignition type.

It will be noted that the fingers 42'and 43'are farther apart than the fingers 44 and 45. This insures that the holding switch HS will always be closed first (before the contacts SC are opened) when the combustion switch heats up and will always open first (before the contacts SC are closed) when the combustion switch cools down. The finger 42 against the blade of the switch SC acts as a stop for the switch actuating arm 36 on temperature reduction and the finger 45 in engagement with the blade of the holding switch HS serves as a stop for the switch arm 31 on temperature rise. After being stoppeclin either direction the clutch illustrated in Figure 2 slips between the surfaces of the collar 34, the arms 36 and 31 and the washer 38 for permitting continued rotation of the combustion switch shaft 32 after theswitches HS and SC have been operated by an initial reversal in temperature. Stops 36a and 31a may also be provided to prevent excessive movement of the arms 36 and 31 in their opposite direction of rotation. The slot 4445 being narrower. than the slot d243 results in the switch blade for HS being operated before .the switch blade for SC regardless of Whether the rod 32 rotates clockwise or counter-clockwise.

If combustion does not occur within the time for which the safety switch is set the contacts SC will remain closed and the safety switch will trip out thus necessitating remedying the trouble and resetting the safety switch. If combustion does occur, opening of the switch SC will render the safety switch inoperative to perform its shutdown function. I

Upon combustion failure the switch actuating arms 36 and 31 will rotate counterclockwise thus first opening the holding switch HS so that the relay will drop out. The contacts SC then. close for energizing the safety switch heater so that the safety switch time starts running. Closure of the contacts SC however, energizes the relay coil RC and if conditions are such that the burner can start up again, it will re-cycle because the switch actuating arm 3'! will be rotatedclockwise thus re-energizing' the relay holding circuit at the This re-cycling may occur once or a number of times and if the. burner finally operates properly it will not shut down. Each re-cycling however adds heat to the safety switch heater and this may cause the safety switch to operate, or temperature in the combustion chamber may not come up fast enough to open the contacts SC on an attempted re-cycling until the safety switch time has run out, whereupon the safety switch will trip and require manual resetting after the cause for the trouble has been discovered and removed. Thus I have provided a control which will normally re-cycle and put the burner back into operation but in cases where combustion is not re-es-tablished lock-out will occur and thus render the operation of the burner entirely safe.

Some changes may be made in the construction and arrangement of the parts of my system Without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims any modified forms of structure or use of mechanical equivalents which may be reasonably included within their scope.

I claim as my invention:

1. In a burner control system: a transformer; a room thermostat; means including a relay operable upon energization to cause operation of the burner; a circuit including the secondary of said transformer and said relay, and controlled by said room thermostat; a first combustion responsive switch closed upon establishment of combustion; a second circuit including said first combustion switch, relay, thermostat and a portion of said secondary to maintain said relay energized from said portion only of said secondary; a second combustion responsive switch in said first circuit and normally closed but opened upon the establishment of combustion after closing of said first combustion switch; a safety shut-down switch controlling energization of said transformer and having an actuating element in said first circuit; and means for operating said combustion switches comprising a temperature actuated movable member, a first combustion responsive operator frictionally driven thereby, a second combustion responsive operator also driven thereby; said operators having means forming lost-motion connections with their respective switches; the lost motion of said first operator being less than that of said second operator to effect operation of said first combustion responsive switch ahead of said second combustion responsive switch when said temperature actuated movable member responds to both temperature rise and temperature fall.

2. In a burner control system: a transformer; an initial room thermostat circuit energized by the secondary of said transformer and including a room thermostat, means including a relay operable upon energization by said secondary to initiate operation of the burner, a safety switch heater, and combustion switch contacts, said combustion switch contacts being opened upon establishment of combustion; a combustion responsive member; slip-friction and lost-motion means connecting said combustion responsive member to said contacts; a safety switch controlling energization of said transformer and normally closed; an actuator for opening said switch when heated by said safety switch heater upon energization thereof for a predetermined period of time; and a second circuit energized by a portion only of said secondary of said transformer and including said room thermostat and said relay, and holding contacts for establishing said second circuit for thereby maintaining said relay energized when said combustion switch contacts are separated; slip-friction and lost motion means connecting said combustion responsive member to said holding contacts; the lost motion in the connecting means for said combustion switch contacts being greater than for said holding contacts to effect operation of said holding contacts ahead of said combustion switch contacts when said combustion responsive member responds to both temperature rise and temperature fall.

3. In a burner control system: a transformer; an initial room thermostat circuit energized by the secondary of said transformer and including a room thermostat, means including a relay operable upon energization by said secondary to initiate operation of the burner, a safety switch heater, and combustion switch contacts, said combustion switch contacts being opened upon establishment of combustion; a combustion responsive member; slip-friction and lost-motion means connecting said combustion responsive member to said contacts; a safety switch controlling energization of said transformer and normally closed; an actuator for opening said switch when heated by said safety switch heater upon energization thereof for a predetermined period of time; a second circuit energized by a portion only of said secondary of said transformer and including said room thermostat and said relay, and holding contacts for establishing said second circuit for thereby maintaning said relay energized when said combustion switch contacts are separated; slip-friction and lost motion means connecting said combustion responsive member to said holding contacts; the lost motion in the connecting means for said combustion switch contacts being greater than for said holding contacts to effect operation of said holding contacts ahead of said; combustion switch contacts when said combustion responsive member responds to both temperature rise and temperature fall, and an ignition switch for the ignition mechanism of said burner opened by said first slip-friction lost-motion means.

4. In a burner control system: a transformer; an initial room thermostat circuit energized by the secondary of said transformer and including a room thermostat, means including a relay operable upon energization by said secondary to initiate operation of the burner, a safety switch heater, and combustion switch contacts, said combustion switch contacts being opened upon establishment of combustion; a combustion responsive member; slip-friction and lost-motion means connecting said combustion responsive member to said contacts; a safety switch controlling energization of said transformer; spring means urging said switch to opened position, a bimetallic latch element in thermal proximity to said heater and operable to release said safety switch when heated to predetermined temperature; and a second circuit energized by a portion only of said secondary of said transformer and including said room thermostat and said relay, and holding contacts for establishing said second circuit for thereby maintaining said relay energized when said combustion switch contacts are separated; slip-friction and lost-motion means connecting said combustion responsive member to said holding contacts; the lost motion in the connecting 7 means for said combustion switch contacts being REFERENCES CITED greater than for Sam holdmg contacts to effect The following references are of record i i-i tlie operation of said holding contacts ahead of said fi of this. patent: combustion switch contacts when said combusv tionresponsive member responds to both tem- 5 ED STATES PATENTS pera-ture rise and temperature fall. Number Name Date i 2,021,407 Erickson e Nov. 1-9, 1 935 PAUL SCHELL. 2,080,580 Shaw .s May 18, 1937 2,274,177 Wilson Feb. 24, 1942 

